Monday morning, December 15, 2014, dawned fine in Sydney. Inside the Lindt Chocolate Cafe on the corner of busy Martin Place and Phillip Street, an early trickle of customers were coming in for coffee and catch-ups with colleagues from the surrounding banks and legal offices. Others were filling in time before appointments or shopping trips. Christmas would arrive in just 10 days.

Fifty-two year old Louisa Hope and her elderly mother Robin had dropped into the cafe for tea and toast, ahead of a meeting with their legal adviser .

Young Elly Chen, who was reporting for just her third shift as a waitress, was already hard at work, along with seven other staff members.

In total, 18 people were going about their ordinary business inside the cafe at 9.40am when serial criminal and would-be sheikh Man Haron Monis pushed aside his chocolate cheesecake, called manager Tori Johnson over for a whispered conversation, rose from the table, pulled a sawn-off shotgun out of his bag and announced he was taking them all hostage in the name of Islamic State.

By the time the siege ended 17 hours later, three people were dead or dying inside the shattered interior: Tori Johnson, executed at point-blank range by Monis; mother-of-three and barrister, Katrina Dawson, fatally wounded by ricocheting bullet fragments from police weapons; and Monis himself, sprawled on the cafe floor with a portion of his head blasted away by the M4 rifles of the police assault team. Four others - three hostages and one police officer - were wounded.

Lying in her hospital bed seven days later, Louisa Hope would tell police about the hellish final seconds of the siege.

"He shot Tori, he assassinated him ... then everything just started to go off," she said, nursing multiple shrapnel wounds.

"I'm trying to cover my face, at the same time trying not to move, there's all this shrapnel coming up from everywhere because everything's being shot up, and it's all in a split second like a car accident ... then you guys come running in, [saying] 'you're safe, you're safe' [but] all the things are flying everywhere still and I'm thinking, not so safe really ... I'm aware that I'm still alive. And I knew that Tori was dead."

In the immediate aftermath, a carpet of floral tributes bloomed across Martin Place.

But the questions soon started coming. Had police waited too long to storm the cafe? How clinical had their emergency entrance been, given that of the six hostages still inside at the end, two were dead and three wounded? Why was there such a barrage of light and noise, with police hurling 11 "flashbangs" or stun grenades - each going off nine times - as they burst into the cafe? Why hadn't the authorities called in the army's highly trained commando forces stationed on Sydney's perimeter? Why was Monis roaming free in the first place, with a string of criminal charges outstanding against him? How effective was police leadership on the night? And how was it that "a mentally deranged individual of low-level capability", as one seasoned counter-terrorism source put it, was able to tie up the state's forces for 17 hours?

Two-and-a-half years later, after one of the most complex inquests in state history, NSW coroner Michael Barnes will on Wednesday hand down his report on what really happened that night.

An army of lawyers has mobilised to represent the often conflicting interests of those affected: the families of Tori Johnson and Katrina Dawson, surviving hostages, the NSW police force, individual supervisors who made key decisions that night, the office of the Director of Public Prosecutions, ASIO, the NSW Justice department and the Defence department.

Barnes' long-awaited report is unlikely to get to the bottom of every tangled narrative flowing from that night. Nor will anything bring back those who died. But it may bring some small measure of relief to the families and survivors. And it will crystallise the lessons that must be learnt for the future, particularly in relation to six critical questions.

1. Why was Monis at large at the time of the siege?

Man Haron Monis outside court in 2010. Photo: AAP

When Monis walked into the Lindt cafe in December 2014, he was already on bail for a staggering 43 counts of sexual assault and for being an alleged accessory to murder. Some of those allegations stretched back to 2002, lodged by women he'd preyed on while running a so-called spiritual healing business. The murder charges had been hanging over his head since November 2013, when his then partner Amirah Droudis??? had been charged with savagely killing Monis' former wife - a murder the trial judge later found Monis had instigated.

The inquest revealed that since arriving in Australia from Iran in 1996, Monis had been on ASIO's radar many times, but at the time of the siege was no longer assessed as a risk to national security. He'd previously scripted a number of extremist videos and declared a fatwa against Barack Obama. He'd been convicted of sending offensive letters to the families of Australian servicemen killed in Afghanistan, and only days before the Lindt attack had lost a constitutional challenge in the high court against that conviction. The National Security Hotline had received no less than 18 calls about him in the week leading up to the siege.

His bail history was equally troubling. Three times he'd been granted bail in the year prior to the siege, despite police opposition.

Police were particularly frustrated when the Office of the Director of Public Prosecutions told them there were no strong grounds to seek Monis' detention after a fresh set of sexual assault charges were slapped on him in October 2014 - just two months prior to the siege. The inquest would hear the solicitor handling the case had only recently joined the organisation and had never before dealt with a bail application in NSW. But neither he, nor the police, were aware Monis had committed some of the assaults while on bail for the federal letter-writing offences.

Counsel assisting the inquest, Jeremy Gormly,??? SC, flagged that failure to link Commonwealth and NSW data on Monis' history of offending was among the key reasons why Monis was out of custody at the time of the Lindt siege.

"It is hard not to note the price we pay for difficulties in the flow of information at jurisdictional borders," he noted.

2. Why did police wait for the death of a hostage before entering the cafe?

Police outside the cafe during the siege. Photo: Daniel Munoz

This question has gnawed incessantly at the Dawson and Johnson families and surviving hostages, especially when it was revealed at the inquest that not all police officers had endorsed the "wait it out" approach. Inside the cafe, the hostages had felt increasingly abandoned as the hours dragged by with no sign of rescue. All their efforts were centred on pacifying Monis, as he made repeated threats to kill one or more of them if there were further escapes (five had fled the cafe during the afternoon).

"We felt like nobody cared about us," hostage Marcia Mikhael said in her police statement.

Forensic psychiatrist Dr Jonathan Phillips later told the coroner that Monis' record "should have defined him as extremely dangerous" but on the night, the most senior officers clung doggedly to a strategy of waiting him out.

Why? One reason was Monis' claim that he was carrying a bomb in his backpack. But there was also the police mindset of "contain and negotiate", deeply embedded in the force's philosophy.

"Time is my friend in these situations," the police forward commander told the coroner several times.

When tactical assault teams stormed the cafe at 2.14am on December 16 it was in response to Johnson's execution, a crisis response known in police parlance as an "Emergency Action" or EA. .

But the inquest revealed officers further down the chain of command had also wanted their chiefs to approve a so-called "Deliberate Action" (or DA) plan - one that would allow them to strike pre-emptively, should a chance arise to catch Monis off-guard.

Three times that night they put a DA plan to their superiors, only to be knocked back each time.

The tactical commander (whose name was suppressed at the inquest) told the coroner such a knockback had never happened to him before.

Indeed Chesterman testified that he'd been unable to see any "rational basis" for the failure to approve a DA, and that in the shoes of the police commandos he would have been "absolutely screaming out" for one to be in place.

Was it actual death or serious injury of a hostage? Or the imminent threat of death or serious injury? Or something else again, perhaps a shot from within the stronghold? Officers seemed unsure, with some changing their evidence as the inquest went on.

Escaped hostage Paolo Vassallo later told the coroner: "It was never going to be a happy ending, a peaceful resolution was never on the cards ... I wanted police to end it on their terms, at least then people would have had half a chance."

3. What were the deficiencIes of training and equipment on the night, and how did they affect the outcome?

For much of the siege, the police negotiating team was equipped with only a landline, a mobile phone and three dictaphones. Even these did not work properly - or were handled ineptly - because 12 batches of hostage calls were lost and never transcribed.

The negotiators spent the first three hours of the siege working from a 4WD because their storm-damaged specialist truck had been out of service since 2011. (It was replaced only late last year.)

When the negotiating team later moved to the nearby Leagues club, they had only one landline between them. This meant missing some hostage calls that diverted elsewhere when the line was busy. Meanwhile the officer in charge of negotiators, who gave evidence under the pseudonym "Graeme", was remotely managing no less than four other stand-offs around NSW while also handling the Lindt crisis over the course of a 33-hour shift.

A British expert who reviewed the negotiating strategy was damning, suggesting the negotiators had gone "in circles" for hours without re-assessing their tactics.

Contrary to public assurances from senior police that contact had been made with the gunman, the negotiating team never managed to deal directly with Monis, who instead was ordering the hostages to deliver messages via media outlets.

The inquest heard that police negotiators failed to try a range of alternative strategies such as using loudhailers, bringing in potential intermediaries such as Monis' former lawyers, issuing appeals from the gunman's family, or carefully crafted public messages from the premier and then police commissioner Andrew Scipione.

Opportunities to bargain with Monis had also been missed. One was his relatively innocuous but persistent demand that the lights in Martin Place be deactivated when night fell. Despite police knowing of this demand for hours - even, at one point assembling (then dismissing) an Ausgrid team to achieve it - the request had not been acted on by the time the siege ended. Yet hostage Selina Win Pe had repeatedly called police from inside the cafe between around midnight and 1am to say Monis was threatening to shoot at least one hostage if the lights remained on.

A consultant psychiatrist advising police on the night (whose name has been suppressed) later claimed some of the Lindt captives had shown signs of Stockholm syndrome, demonstrating "excessive and gratuitous alliance with the hostage taker". The claim outraged surviving hostages. "We were just trying to stay alive," one told Fairfax Media.

4. What was the impact of communication failures on the night?

Tori Johnson sent a text message to his family half-an-hour before he died saying Monis was "increasingly agitated, walks around when he hears a noise outside with a hostage in front of him. Wants to release one person in good faith, tell police". Yet the police commander during the final hours of the siege, Assistant Commissioner Mark Jenkins, told the coroner he was not made aware of the text.

Nor was Jenkins aware that when Monis fired the first shot after a group of hostages who escaped at 2.03am, it was almost certainly aimed at them, and not over their heads. "If I was convinced the shot was made directly at hostages then yes, I would have thought an EA should have been activated ??? but I was not told that at the time and I don't know that to be the case today," Jenkins told the inquest.

Mark Murdoch, who had occupied the top police command role earlier in the day, said if the 2.03am shot at the hostages had been fired on his watch, "I would have had an expectation that the EA would have been launched."

Intermittent faults in radio communication between the various police teams also seem to have had a critical bearing on the last few minutes of the siege.

When Johnson was forced into a kneeling position at 2.06am, hands laced behind his head, a sniper codenamed Sierra 3-1 sounded the alert over the radio but heard no acknowledgement and did not repeat the call, he told the coroner.

Another officer, the commander of the assault teams, said if he had known of Johnson's plight at that time he would have recommended an immediate assault.

Further questions have been raised about the high-powered ammunition and weapons that the Tactical Operations Unit used in storming the cafe. Some experts have questioned whether lower-velocity bullets less prone to fragmentation should have been used in such a confined space.

5. Should the army have taken over the siege when it became plain progress had stalled?

Much of what transpired between the police and the military that night remains veiled, thanks to secrecy orders sought by the Commonwealth. Australian Defence Force advisers were positioned at the police command posts during the siege. And the army's commando squad, the Tactical Assault Group-East based at Holsworthy in outer Sydney, did start to mobilise, constructing some kind of mock-up of the Lindt cafe and consulting with NSW Police on the the latter's plans. TAG-EAST had battle-hardened soldiers in its ranks, highly practiced at forcing their way into enemy strongholds.

But the army commandos were never called in and at the inquest later, the ADF pointedly played down its role. Gormly told the coroner he was unlikely to get to the bottom of how the relationship between the Commonwealth and NSW authorities really played out that night.

Similarly, the inquest only heard in February this year that the Australian Federal Police had compiled secret reports on Monis' alleged backpack bomb but that these had not been transmitted to NSW police. The revelation came so late in the hearings, there was little opportunity for the coroner to test its significance.

At least one hostage, Paolo Vassollo, told police shortly after his escape four hours into the siege that he gave no credibility to Monis' claim of having a bomb. "From the way he was talking and acting, I didn't believe him," Vassallo told the coroner.

Likewise Louisa Hope also later told police that the backpack Monis wore throughout the siege, (later shown to have housed a speaker, not a bomb), "didn't look packed ... It didn't look like it was full or heavy or hard to manage".

What sort of intelligence was marshalled to test Monis' claim of carrying a bomb is another mystery. Yet the bomb fear dictated nearly every aspect of police tactics that night.

6. How effectively did senior police leadership respond?

Deputy Commissioner Catherine Burn, who had organisational responsibility for counter-terrorism, came under sustained questioning over her deletion of text messages from the night. She went home, with permission, well before the siege had come to an end. In the witness box she insisted she'd had no operational role, instead being tasked with high-level liaison with politicians and other agencies. In April this year, Burn was moved from counter-terrorism by newly appointed police commissioner Mick Fuller.

Then commissioner Andrew Scipione gave evidence that he'd had no formal role in the direction of the siege either. Yet he did have communications with senior commanders on the night, including a discussion about taking down YouTube videos that had been directed by Monis and posted by the hostages. Despite sending an email saying the videos should be "pulled down", Scipione denied that this was an order.

The inquiry would later hear that the absence of the videos could have contributed to rising tensions inside the cafe, as Monis grew increasingly frustrated by the failed efforts of the hostages to get messages out via social media. The inquest also heard that late at night on December 15, Scipione and Assistant Commissioner Jenkins discussed whether a DA should be a "last resort" - but both men denied this suggestion came from Scipione.

The Lindt siege report is likely to accelerate the rethink already under way in Australian counter-terrorism circles about how to respond to extremist-inspired terrorism. Almost certainly the "contain and negotiate" philosophy will be ditched in favour of swift intervention, senior sources told Fairfax Media.

One official believes the Lindt siege lends itself to the same "Swiss cheese" analogy used by investigators in aviation accidents: that if all the holes in the slices line up, you get a crash.

"Lindt cafe was like that," the experienced counter-terrorism source claims.

"Each slice of cheese had a hole: a policy slice, the communications slice, the equipment slice, a leadership slice and an intelligence slice - all the holes in all those things lined up and so we had Lindt. If NSW law enforcement was unable to deal with that lone individual, one has to ask, are they ready for a multiple location, multimodal attack? I think it's a huge vulnerability for NSW and it still is."

We will soon know if the coroner takes a similar view.

CCTV footage of police entering the cafe.

How it happened: a timeline

Monday, December 15

6.30am Tori Johnson is at work, having coffee with staff member Harriette Denny.

8.15am Barrister Katrina Dawson picks up her friend and pregnant colleague Julie Taylor for the trip into the city, arranging to meet later for coffee.

9.15am Dawson arrives, followed soon afterwards by Taylor and their solicitor friend Stefan Balafoutis. Fifteen other staff and customers are also in the cafe.

9.35 to 9.40am Monis calls manager Johnson over, sits huddled with him for a few minutes, orders him to get the keys and lock the doors. Monis puts on his vest and bandanna.

9.41am Tori calls triple zero relaying Monis' claim that he has bombs in three locations, that its an Islamic State attack and Monis wants to speak to then prime minister Tony Abbott. Monis pulls a sawn-off shotgun from a large blue Big W bag.

9.50am Monis orders hostages to place phones on tables and stand with their hands up in the windows. Instructs them to contact media outlets, warning he has a bomb in his backpack.

10.00am First police negotiator arrives at scene along with first police commando team.

Mid-morning NSW Police invoke anti-terrorism protocols, set up a forward command post and a police operations centre to manage the siege, brief state and federal cabinet.

5.00pm Second escape: April Bae and Elly Chen who have been hiding under a table slip out a side door and escape unnoticed by Monis.

7.05pm Vassallo receives a text from Johnson: "Tell the police the lobby door is unlocked. He's sitting in a corner on his own."

8.20pm Commander of the Tactical Operations Unit wants a Deliberate Action (DA) plan approved to allow police to storm Monis at a time of their choosing, instead of waiting for a hostage to be wounded or killed; request knocked back by senior police. Monis becoming increasingly agitated as attempts to get his message out via the hostages using social media are thwarted.

10.57pm Phone call between Jenkins and then police chief Andrew Scipione. A scribe records: "DA plan to occur as last resort - COP (Commissioner of Police)"; Jenkins and Scipione both later deny this was an order from Scipione.

11pm Monis tells hostages to call loved ones.

Tuesday, December 16

12.35am Hostage Selina Win Pe starts calling negotiators saying Monis will shoot someone if lights in Martin Place are not turned off. She warns: "I'm going to get shot in 15 minutes if you don't have these lights switched off."

1.30am Monis toys with releasing one of the remaining 13 hostages to talk to media, but is growing increasingly erratic.

1.43am Text from Johnson to his family saying Monis is "increasingly agitated, walks around when he hears a noise outside with a hostage in front of him. Wants to release one person in good faith, tell police."

2.00am Monis hears a noise and goes to kitchen to investigate, taking two hostages with him.